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Today I would like to share something on Mechanical vibration. We may not be able to see complete Modal and vibration analysis, I would like to keep it simple. I think before doing modal analysis on any FEM software, it is very essential that you understand the basic concepts of Mechanical vibration.
So lets refresh our memories,by pulling out some definitions what we studied in Engineering college.
What is Vibration?
Vibration in simple terms is said to be mechanical oscillation about a equilibrium point. The oscillation may be periodic or random based on the application.
Any vibration has two measurable quantities namely amplitude and frequency.
When a body vibrates, the free end of the object moves to maximum position and returns back to equilibrium point once again it moves in a opposite direction. The displacement from equilibrium position to Maximum position it moved is called amplitude. And how fast (frequency) the object moves helps determine its vibrational characteristics.
Frequency
A vibrating object moves back and forth from its normal stationary position. A complete cycle of vibration occurs when the object moves from one extreme position to the other extreme, and back again. The number of cycles that a vibrating object completes in one second is called frequency. The unit of frequency is hertz (Hz). One hertz equals one cycle per second.
Amplitude
A vibrating object moves to a certain maximum distance on either side of its stationary position. Amplitude is the distance from the stationary position to the extreme position on either side and is measured in metres (m). The intensity of vibration depends on amplitude.
What is resonance?
Every object tends to vibrate at one particular frequency called the natural frequency. The measure of natural frequency depends on the composition of the object, its size, structure, weight and shape. If we apply a vibrating force on the object with its frequency equal to the natural frequency, it is a resonance condition. A vibrating machine transfers the maximum amount of energy to an object when the machine vibrates at the object's resonant frequency.
From the engineering point of view:
Should we care about vibrations ? Yes off course, vibrational loads could cause fatigue and induce high stress which would damage the whole system.
One could feel the vibration by noise it generate or even we can feel it from any mechanical systems like washing machine, automobile engine etc.,
We could see vibration occurs in two categories either as free vibration or forced vibration.
Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely.
Forced vibration is when an alternating force or motion is applied to a mechanical system.
Causes of mechanical vibration may be due to following reasons:
- Unbalanced forces in rotating systems.
- Elasticity and mass of system
- Misalignment of parts.
- Broken gear teeth's(wear and breakage).
- Weak or Bend shafts.
- Due to faulty joints.
- Improper maintenance of Bearnings.
And there are many more reasons which may lead to vibration forces. As an Engineer we can overcome this by providing damping,altering structure,size and mass properties.
With this we will end this session. Hope you enjoyed it.
Sources: Mechanical vibration causes and effects to humans
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